In electrostatographic imaging and recording processes such as electrophotographic copying, an electrostatic latent image formed on a photoconductive surface is developed with a thermoplastic toner powder, which is thereafter fused to a receiver. The fuser member can be a roll, belt or any surface having the suitable shape for fixing thermoplastic toner powder to the receiver. The fusing step commonly consists of passing the receiver, for example, a sheet of paper on which toner powder is distributed in an imagewise pattern, through the nip of a pair of rolls. At least one of the rolls is heated; in the case where the fuser member is a heated roll, a smooth resilient surface is bonded either directly or indirectly to the core of the roll. Where the fuser member is in the form of a belt, it is preferably a flexible endless belt having a smooth, hardened outer surface that passes around the heated roller. A persistent problem with electrostatographic fusing systems, known as offset, is the adhesion of heat-softened toner particles to the surface of the fuser member rather than the receiver during passage through the rolls. Any toner remaining adhered to the fuser member can cause a false offset image to appear on the next sheet that passes through the rolls and can also degrade the fusing performance of the member. Another possible problem is degradation of the member surface caused by continued heating, which results in an uneven surface and defective patterns in thermally fixed images.
Toner fuser rolls are composed of a cylindrical core that may include a heat source in its interior, and a resilient covering layer formed directly or indirectly on the surface of the core. A thin layer of a suitable primer is may be coated on the surface of the core in order to improve bonding of the layer. Roll covering layers are commonly made of fluorocarbon polymers or silicone polymers, for example, poly(dimethylsiloxane) polymers of low surface energy, which minimizes adherence of toner to the roll. Frequently, release oils such as poly(dimethylsiloxanes) are also applied to the fuser roll surface to prevent adherence of toner to the roll. Such release oils may interact with the resilient layer upon repeated use and in time cause swelling, softening, and degradation of the roll. Silicone rubber covering layers that are insufficiently resistant to release oils and cleaning solvents are also susceptible to delamination of the roll cover after repeated heating and cooling cycles.
Toner fuser belts are composed of a continuous flexible material having superior resistance to heat and a smooth surface. The belt substrate can be metallic or polymeric. The surface of the belt is composed of a thinly coated, low surface energy polymer such as a fluorocarbon or a silicone resin. There is a need for coating compositions which adhere strongly to the belt and form a hard, tough surface that is resistant to wear and cracking. The surface should also be resistant to cleaning solvents and fluids.
In electrostatographic imaging processes dry developers can be used to form an image on a receiving surface such as a sheet of paper. Dry developers usually comprise a toner powder and carrier particles. Carrier particles and toner particles have different triboelectric values. As the developer mixture is agitated, the particles rub together and the toner and carrier particles acquire opposite electric charges and cling together. In the subsequent development step the somewhat higher opposite charge of the electrostatic latent image draws the colored toner from the carrier and develops the image. Various addenda are frequently used to improve the properties of the toner and carrier particles.
Toners comprise, as a major component, the binder and, as minor components, a colorant and a charge control agent. The binder can be any resin having properties suitable for dry toners. Many such resins are known, but thermoplastic resins that are fixable by fusing are especially useful. When a dry toner powder image is transferred from one surface to another, defects in the image can occur. U.S. Pat. No. 4,758,491 teaches that the addition of low surface energy addenda, especially polymers containing organopolysiloxane segments, may alleviate such defects.
Carrier particles comprise magnetizable irregular particles that are usually coated with a film of a polymeric material, which helps develop the triboelectric charge and aids the transfer of the toner. The coating material must adhere well to the carrier particle because the toner charge decreases as the polymer wears off. Polymers with low surface energy properties are especially useful for coating carrier particles.
Recent electrophotographic apparatus and processes are disclosed in U.S. Pat. Nos. 5,089,363 and 5,411,779, the disclosures of which are incorporated herein by reference. U.S. Pat. No. 5,411,779 describes an apparatus having an image-fixing belt with a polyimide resin inner layer and a fluoroplastic outer layer that produces unglossed, matte images. Other fuser belt systems are described in U.S. Pat. Nos. 5,200,284; 5,233,008; 5,330,840; 5,362,833; and 5,529,847, the disclosures of which are incorporated herein by reference.
The ferrotyping belt used for the production of high gloss toner images typically consists of a metal or an organic polymeric substrate on which is coated a release layer. The toner is generally fused in a heated nip to a receiver, which then continues to travel along the belt without releasing until the toner is cool. To avoid the use of a release oil, the release layer of the fuser belt must have low surface energy.
Toner fuser belts are composed of a continuous smooth, heat-resistant, flexible material on a metallic or polymeric substrate. A release layer applied to the belt substrate is a thinly coated, low surface energy polymer such as a fluorocarbon or a crosslinked silicone resin. Such release layers, however, often display poor mechanical properties, including inadequate adhesion to the metal support, and are susceptible to rapid wear upon repeated contact with abrasive receiving sheets such as bond paper or uncoated laser print paper.
There remains an ongoing need for fuser belts having durable surface layer compositions that adhere well to the substrate, form a hard, tough surface that is resistant to wear, cracking and solvents, and are capable of producing multiple high quality, high gloss toner images, including multicolor images. This need is well met by the toner fuser belt of the present invention.